1. Field of the Invention
The present invention relates to an active device array substrate and fabricating method thereof. More particularly, the present invention relates to a thin film transistor array substrate and fabricating method thereof.
2. Description of Related Art
Most displays are designed to provide their users with the greatest viewing comfort. Therefore, a central issue for the manufacturers is to remove as many defects that are detectable by human vision as possible. Using liquid crystal display as an example, a liquid crystal display is manufactured through a series of complicated processes involving at least the fabrication of backlight module, liquid crystal layer and two pieces of substrates. If a small defect appears in one of the processes, quality of the display panel may be adversely affected and visible defects may appear in the final light-on test. One such viewing defect is the so-called ‘mura effect’, for example.
In addition, an organic material layer is frequently formed over the thin film transistor array substrate of a liquid crystal display to planarize the uneven steps between various devices so that subsequent alignment of the alignment film can be performed smoothly to reduce the probability of alignment defects. The display quality of the panel is closely related to the alignment of the liquid crystal molecules in the alignment engineering. In general, most organic material layer has a smooth and planar surface. Hence, in the presence of even a small defect after the liquid crystal alignment process, overall display quality of the liquid crystal display panel may be significantly affected.
At present, one method of lowering or eliminating mura effect due to defects in the fabrication process includes forming cavity patterns on the surface of an organic material layer with a photolithography process. Since the cavity patterns on the surface of the organic material layer can provide the liquid crystal molecules with different pre-tilt angles in molecular alignment, mura effect is eliminated or lowered. However, the foregoing photolithography process for forming the concave patterns is achieved by exposing the organic material layer through a half-tone photomask and developing the organic material layer thereafter, which is an expensive process. Furthermore, the dimension of the concave patterns produced by the half-tone photolithography process is limited by the resolution of the current stepper machine to the micrometer scale. It is difficult to produce concave patterns on a finer scale. Because the liquid crystal molecules have a dimension in the nanometer scale, the process that can produce nanometer scale concave patterns on the surface of an organic material layer would reduce or lower the mura effect more obviously.